If Mojang releases a 1.21.x hotfix, the pack might break. Always check the source site for a "hotfix" version of the pack. Conclusion
Launch Minecraft and go to (for all worlds) or click the Edit (pencil icon) next to a specific world. Scroll down the left sidebar to Resource Packs . Click on My Packs . Find Actions & Stuff , click it, and select Activate .
Ensure it is at the top of your "Active" list to prevent other packs from overwriting the animations. Troubleshooting Common Issues
You may need 7-Zip or WinRAR, though Windows handles .mcpack files natively.
Minecraft Bedrock Edition has evolved significantly, but for many players, the "stiff" animations of the default character models leave something to be desired. If you are looking to breathe life into your game, the resource pack is the gold standard.